# Type Declarations
> TypeScript type declarations for stdlib.
## Usage
```typescript
///
import { ArrayLike } from '@stdlib/types/array';
function sum( x: ArrayLike ): number {
let s = 0.0;
for ( let i = 0; i < x.length; i++ ) {
s += x[ i ];
}
return s;
}
```
Type declarations are organized as modules. For example, to use iterator type declarations,
```typescript
///
import { Iterator } from '@stdlib/types/iter';
function sum( iter: Iterator ): number {
let s = 0.0;
while ( true ) {
let v = iter.next();
if ( v.done ) {
break;
}
s += v.value;
}
return s;
}
```
For the complete list of declared modules, see the `index.d.ts` type declaration file.
## Notes
- In order to use included TypeScript declarations, configure your `tsconfig.json` file accordingly. For example,
```text
{
"compilerOptions": {
...
"typeRoots": [ "./path/to/@stdlib/types" ],
...
},
...
}
```